Thermodynamics of complex formation between Cu(II) and glycyl–glycyl–glycine in water–ethanol and water–dimethylsulfoxide solvents

The paper provides an overview of own data on complex formation between Cu(II) and glycyl–glycyl–glycine in water and water–organic mixed solvents. Calorimetric and potentiometric methods were employed for the study of complex formation between Cu(II) with zwitterion of glycyl–glycyl–glycine and anion of glycyl–glycyl–glycine in water–ethanol and water–dimethylsulfoxide solvents. Stability of [CuHL]2+ and [CuL]+ grows with increase in concentration of both non-aqueous components in solvents. A monotonic increase in the exothermicity of [CuHL]2+ complexation with the addition of ethanol to water was observed. The enthalpy of [CuL]+ complex formation has changed with an exothermic peak at 0.1 ÷ 0.3 mol fractions of ethanol. The main solvation contributions which control the exothermicity increasing of [CuL]+ complex formation reaction and the stability of [CuHL]2+ in H2O–EtOH solvent were not established. However, the resolvation of ligands is the key factor for growth of the stability of both [CuHL]2+ and [CuL]+ complexes in H2O–DMSO solvent as well as the stability of [CuL]+ and the exothermicity of [CuHL]2+ complex formation in H2O–EtOH mixtures. Proper data are compared with data reported in the literature.